Polyester polymers have developed considerable interest due to their excellent physical properties and low manufacturing costs. However, many of the most widely used polyester polymers, such as polyethylene terephthalate, are not biodegradable and can have long lasting environmental consequences.
To cope with these problems, much effort has been focused on developing polymer materials that, when discarded and left in the environment, are naturally degraded by microorganisms and/or other natural factors into harmless materials.
A number of biodegradable polyester polymers have been developed from naturally derived feed stocks as well as synthetic or semi-synthetic precursors.
One such biodegradable polyester is polylactic acid (or polylactide), which has garnered considerable interest owing to the fact that it can be mass-produced from renewable resources, such as corn starch and sugar cane and its useful physical properties.
Enantiopure polylactic acid is a crystalline thermoplastic material that has tensile strength equivalent to that of polyethylene and transparency equivalent to that of polyethylene terephthalate. Importantly, polylactic acid readily degrades when discarded in the environment into lactic acid, carbon dioxide, and water, all of which are essentially environmentally harmless.
Despite the many desirable physical properties exhibited by polylactic acid, its inherent brittleness and notch sensitivity pose a considerable scientific challenge and limit its large-scale application as a structural material.
Accordingly, there exists a need to develop methods for toughening polyester polymers, such as polylactic acid, which do not compromise the strength, stiffness, and transparency of the polymer.